1. Field of the Invention
The present invention relates generally to a semiconductor device and a method of manufacturing the semiconductor device, and the invention is applicable to, for example, a gate insulation film of a MOSFET (Metal Oxide Semiconductor Field Effect Transistor).
2. Description of the Related Art
With development in fine patterning of semiconductor devices in recent years, the thickness of a gate insulation film has been decreased more and more. Consequently, there arises a problem of an increase in so-called off-leak current. That is, even when no voltage is applied to the gate electrode, carriers pass through the gate insulation film and a leak current occurs. It is thus necessary to reduce the off-leak current by increasing the effective film thickness of the gate insulation film. As a method for achieving this, there has been an attempt to apply a high-dielectric-constant material (so-called High-k material) to the gate insulation film.
If the high-dielectric-constant material is applied to gate insulation film, however, oxygen in the high-dielectric-constant material diffuses into the silicon substrate, and a thin SiO2 layer forms at an interface between the silicon substrate and the high-dielectric-constant material. As a result, the dielectric constant, as a whole, is determined mainly by the SiO2 layer. Thus, the dielectric constant of the entire gate insulation film is not effectively improved, nor is a stable interface with the silicon substrate formed (see, e.g. Z. Yu, J. Ramdani and J. A Curless et al., “Epitaxial oxide thin films on Si(001)”, J. Vac. Sci. Technol. B 18(4) (2000) 2139, and G. B Alers, D. J. Werder and Y. Chabal et al., “Intermixing at the tantalum oxide/silicon interface in gate dielectric structures”, Appl. Phys. Lett., 73 (1998) 1517).
On the other hand, in order to form a thermodynamically stable interface between the silicon substrate and gate insulation film, studies have vigorously been made to apply a silicate-based oxide film, which includes an SiO2 layer as a matrix, to the gate insulation film. In these studies, particular attention has been paid to (ZrO2)x(SiO2)1-x, (HfO2)x(SiO2)1-x, and (Gd2O3)x(SiO2)1-x systems. Other prospective candidates include (La2O3)x(SiO2)1-x and (Y2O3)x(SiO2)1-x systems. Since an interface between this kind of silicate material and the silicon substrate is very similar to a conventional SiO2—Si interface, there is a possibility that a high-quality channel region is obtained.
Researches and developments for the above-mentioned silicate-based oxide films have currently centered on amorphous structures. However, the amorphous structure has poor polarizability, and a high dielectric constant can hardly be obtained. Hence, with the above-mentioned silicate-based oxide films, a sufficiently high dielectric constant cannot be obtained (see, e.g. J. A Gupta, D. Landheer and J. P. McCaffrey et al., “Gadolinium silicate gate dielectric films with sub-1.5 nm equivalent oxide thickness”, Appl. Phys. Lett., 78 (2001) 1718, and G. D Wilk and R. M. Wallace, “Electrical properties of hafnium silicate gate dielectrics deposited directly on silicon”, Appl. Phys. Lett., 74 (1999) 2854).